Shock absorber piston

ABSTRACT

A telescopic hydraulic shock absorber for a motor vehicle has a piston of composite construction. The composite piston includes a metal core that is ported to provide jounce and rebound flow passages and a plastic peripheral surface that is in slidable engagement with the pressure tube of the shock absorber.

United States Patent 91 Fouts [451 May 1,1973

[ SHOCK ABSORBER PISTON [75] inventor: Norman G. Fouts, Belleville,Mich.

[73] Assignee: Ford Motor Company, Dearbom,

Mich.

[22] Filed: Apr. 16,1971

[21] Appl. No.: 134,570

[52] US. Cl ..188/322, 92/248 [51] Int. Cl. ..Fl6f 9/32 [58] Field ofSearch ......l88/322, 276;

[56] References Cited 7 UNITED STATES PATENTS 3,212,411 10/1965 Storms..92/248 1,802,281 4/1931 Shimer ..92/249 X 3,136,228 6/1964 Dailey 8/1967 Sheldon ..92/248 Primary Examiner-George E. A. Halvosa AtzomeyJohnR. Faulkner and Clifford L. Sadler 5 7] ABSTRACT A telescopic hydraulicshock absorber for a motor vehicle has a piston of compositeconstruction. The composite piston includes a metal core that is portedto provide jounce and rebound flow passages and a plastic peripheralsurface that is in slidable engagement with the pressure tube of theshock absorber.

6 Claims, 2 Drawing Figures Patented Mg? 1, 1973 I INVEN TQR wok/WW a 00ATTORNEYS BACKGROUND OF THE DISCLOSURE The present invention relates totelescopic hydraulic shock absorbers for motor vehicles, and moreparticularly to the construction of an improved piston for such devices.

It is presently conventional practice in automotive shock absorbers toprovide a cylindrical pressure tube in which a valved piston and rodassembly reciprocates. The valved piston divides the interior of thepressure tube into jounce and rebound pressure chambers. Such a shockabsorber is interposed between the sprung and unsprung components of amotor vehicle and relative movement between these components is clampedby the restricted flow of hydraulic fluid through the control orificesin the shock absorber piston.

In order to obtain the desired degree of control over hydraulic fluidflow between the two pressure chambers, it is desirable to eliminate anyclearance between the piston periphery and the interior wall of the pressure tube. Zero clearance between the piston and pressure tube preventshydraulic fluid flowing from one pressure chamber to the other frombypassing the control valves in the piston by flowing around the piston.

Zero clearance, however, is not practical in the conventional shockabsorber having a metal piston because metal-to-metal engagement of thepiston with the pressure tube wall will result in rapid wear of therubbing components. For that reason, some clearance must be providedbetween the piston and the pressure tube to assure the presence of alubricating film of hydraulic fluid and thereby reduce wear. Theclearance thus provided, however, constitutes a bypass passage in aconventional shock absorber with a resulting reduction in the controlprovided by the pistons control valves and ports.

BRIEF SUMMARY OF THE DISCLOSURE In view of the state of the art, it isthe principal object of the present invention to provide a shockabsorber for a motor vehicle having a piston with a plastic peripheralsurface in slidable engagement with the pressure tube.

In the presently preferred embodiment of this invention, a double actinghydraulic shock absorber is constructed for use in a motor vehicle andhas a piston assembly that reciprocates within a pressure tube. Thepiston assembly includes a piston element of composite construction. Thepiston element has a metal core molded of sintered powder metal withjounce and rebound flow control passages.

The metallic piston core is placed in an injection molding machine and aplastic bearing surface layer is molded about the periphery of thepiston core. The piston core is provided with axially extending upperand lower flanges and the molded plastic bearing surface engages theflanges in an interlocking relationship. The plastic layer is molded toan outside diameter very nearly equal to the inside diameter of thepressure cylinder whereby a minimum clearance is provided. In order topermit the insertion ofthe piston assembly into the pressure tube duringmass production operations, the plastic bearing surface is provided witha cylindrical extension or skirt of reduced diameter that extends belowthe metallic piston core. This extension or skirt functions as a guideand permits the ready assembly of the piston into the pressure tube.

BRIEF DESCRIPTION OF THE DRAWINGS The many objects and advantages of thepresent invention will become apparent upon consideration of thefollowing detailed discussion and the accompanying drawings, in which:

FIG. 1 is an elevational view, in section, of a double acting shockabsorber for a motor vehicle having a piston constructed in accordancewith this invention; and

FIG. 2 is an enlarged sectional view of the composite piston shown inFIG. 1.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENT Referring nowto the drawings, wherein the presently preferred embodiment of thisinvention is illustrated, FIG. -1 discloses a direct acting hydraulicshock absorber 10 for a motor vehicle. The shock absorber 10 includes apressure tube 12 in which a piston assembly 14 is reciprocably mounted.A piston rod 16 has one end connected to the piston assembly 14 and itsother end extending upwardly. Means are provided on the upper end of thepiston rod 16 for connecting it to a sprung component of a motorvehicle.

The upper end of the pressure tube 12 is closed by a rod guide 18 andthe lower end of the pressure tube 12 is closed by a foot valve assembly20. An annular cap member 22 is seated on an annular flange portion 24of the rod guide 18 and has a depending flange 25 to which a reservoirtube 26 is connected. A lower cap 28 is welded to the reservoir tube 26and engages the foot valve assembly 20 at spaced points such as at 30.Attachment means 32 is secured to the lower cap 28 and provides a devicefor connecting the shock absorber 10 to an unsprung component of a motorvehicle suspension system.

The piston rod 16 extends through the rod guide 18 and the cap. 22.Positioned between the cap 22 and guide 18 is a rubber seal 34 that isin slidable sealed engagement with the piston rod 16. A coil spring 36is interposed between the rod guide 24 and the seal 34 to urge the sealinto tight engagement with the piston rod 16.

The piston assembly 14 divides the interior of thepressure tube 12 intojounce and rebound pressure chambers 38 and 40. The jounce chamber 38 issituated between the piston assembly 14 and the foot valve 20. Therebound chamber 40 is of annular shape and is situated between thepiston assembly 14 and the rod guide 18. An annular reservoir chamber 44is defined between the pressure tube 12 and the reservoir tube 26. Thechamber in which the seal spring 36 is situated is in communication withthe reservoir chamber 42 by means ofa port 44 in the flange 24 of therod guide 18. Port 44 permits fluid leaking between the rod 16 and guide18 to be returned to the reservoir chamber 42.

The piston 46 is of composite construction and comprises a metal core 48and a plastic peripheral portion 50. The construction of the plasticportion 50 will be described in greater detail later.

The piston 46 isprovided with a series of rebound ports 52 and a seriesof jounce ports 54. Annular valve seats 56 and 58 are provided on theupper surface of the piston core 48 and are situated inwardly andoutwardly, respectively, of the jounce ports 54. A disc shaped valveelement 60 is pressed into sealing engagement with the valve seats 56and 58. Spring seat 62 engages the valve element 60. A coil spring 64,interposed between the spring seat 62 and a second spring seat 66, urgesthe valve element 60 to a closed position.

The piston 46 is provided with depending annular valve seats 68 and 70on its lower surface that are spaced inwardly and outwardly of therebound passages 52. A disc shaped valve element 72 is seated againstthe valve seats 68 and 70 and is held in that position by a coil spring74 that is interposed between a flanged nut 76 and a spring seat 182which engages the disc 72.

The nut 76 is threaded on the reduced diameter end portion of the pistonrod 16 and serves to hold the several components of the piston assembly14 in their appropriate relative position.

In order to provide a minimum clearance between the piston 46 and theinterior of the pressure tube 12, the plastic portion 50 is provided onthe exterior periphery of the metal core 48. The plastic layer 50 may beformed of nylon or other plastic material having similar properties. Thecore 48 of the piston 46 is provided with an upwardly extending annularflange 80 and a downwardly extending annular flange 82. The plasticportion 50 is molded with a thin layer 83 of uniform thicknesscompletely enveloping the cylindrical periphery 84 of the core 48situated between the annular flanges 80 and 82. In one embodiment of theinvention, the plastic layer 83 covering the periphery of the metalliccore 46 was 0.015 inches in thickness.

The upper surface of the core 48 is provided with a flat annular surface86 that extends in a plane perpendicular to the axis of the piston 46and the plastic portion 50 is molded even with the surface 86. It is tobe noted from FIG. 2 that the limit of the flange 80 is spaced from thesurface 86 so that the plastic portion 50 may flow and be molded into adownwardly extending annular flange 88. This construction provides aninterlocking relationship which secures the upper end of the plasticportion 50 in position.

The plastic portion 50 is also molded in interlocking relationship aboutthe depending flange 82 of the core 48 so as to provide an upstandingcircumferential portion 92 that is spaced upwardly and inwardly of themetal flange 82.

The plastic piston portion 50 includes a depending plastic flange orskirt 94. The flange 94 extends for a length of between one quarter andone fifth of the total axial length of the plastic portion 50. Theflange 94 has a reduced diameter peripheral surface 96 and is ofsufficient thickness to be rigid.

The composite piston 46 is molded with the plastic portion 50 having anoutside diameter that is very slightly less than the inside diameter ofthe tube 12 in order to compensate for manufacturing tolerances in thedimensions of these parts.

OPERATION The plastic portion 50 provides a nonmetallic hearing surfacein slidable engagement with the wall of the pressure tube 12. Because ofthe low friction bearing qualities of the plastic, there is a reducedneed for lubrication and clearance between the piston and the pressuretube.

The portion 83 of plastic 50 is manufactured with an outside diameterthat nearly equals the inside diameter of the pressure tube 12.Therefore, insertion of the piston assembly 46 into the pressure tube 12would be extremely difficult without the presence of the reduceddiameter flange portion 94 which facilitates the assembly of thecomponents.

in one embodiment of the present invention, the pressure tube 12 has anominal diameter of 1.0000 inch with a tolerance of plus or minus 0.0005so that under some manufacturing conditions the pressure tube may havean inside diameter of 0.9995 inches. The piston assembly 46 ismanufactured with an outside diameter in the range of 0.9982 to 0.9975inches. In this one embodiment of the invention, the plastic portion 50is manufactured of nylon which has a propensity to absorb moisture thatwill cause it to swell. The absorption of moisture can cause thediameter of the composite piston 46 to increase by 0.0010 inches sothat, under some manufacturing conditions, the piston assembly 46 mayhave a maximum diameter of 0.9992 inches. The insertion of a pistonhaving an outside diameter of 0.9992 into a pressure tube having aninside diameter of 0.9995 inches provides a clearance of only 0.0003inches. The assembly of these parts would be nearly impossible if itwere not for the reduced diameter flange portion 94 which serves toguide the composite piston 46 into the pressure tube.

The plastic portion 50 provides a superior bearing surface so thatminimal clearance may be provided between the piston 46 and tube 12.With minimal clearance, practically no fluid bypasses the ports 52 and54 during a stroke of the shock absorber and the valving within thepiston assembly 14 provides substantially all of the control over theflow of fluid between the jounce pressure chamber 34 and rebound chamber40.

The valving of the piston 14 operates in a reasonably conventionalfashion. During a compression stroke when the piston assembly 14 istravelling downwardly in the pressure tube 12, the jounce chamber 38will be reduced in size. Fluid will flow from the jounce chamber 38through the jounce flow passages 54 against the resistance provided bythe spring pressed valve element 60. Fluid will also flow from thejounce chamber 34 through the valving of the foot valve 20 to thereservoir chamber 42 in an amount equalto the fluid displaced by thepiston rod 16. The foot valve 20 is similar in construction andoperation to the foot valve described in US. Pat. No. 2,69l,387 to J. N.Strauss.

During a rebound stroke when the piston assembly 14 is moving upwardlyin the pressure tube 12, fluid will be forced from the rebound chamber40 through the rebound passages 52. This fluid flow will be controlledby the spring pressed valve element 72. At the same time, fluid will bedrawn through the replenishing valve passages of the foot valve assembly20 into the jounce chamber 38 from the reservoir chamber 42 in an amountequal to that which was displaced by the plston rod 16 as it iswithdrawn from the pressure tube 12.

Tremendous pressures are created in the shock absorber when it isoperating in a vehicle travelling a rough road. These pressures tend todislodge the plastic portion 50 and extrude it through the gap betweenthe pressure tube and the piston core 48. The unique interlockingrelationship between plastic portion 50 and the core flanges 80 and 82prevents such displacement from occurring.

The foregoing description presents the presently preferred embodiment ofthis invention. Modifications and alterations may occur to those skilledin the art that will come within the scope and spirit of the followingclaims.

Iclaim:

l. A shock absorber for a motor vehicle having a piston reciprocablewithin a pressure tube, said piston being of composite construction andhaving a metallic core with jounce and rebound flow passages, a plasticexterior layer surrounding the peripheral surface of said metallic core,said plastic layer having a cylindrical surface in slidable engagementwith said pressure tube,

said surface having an exterior diameter substantially equal to theinterior diameter of said pressure tube whereby only minimal clearanceis provided between said piston and said tube, said plastic layer havinga depending annular flange of substantial length relative to the totallength of said plastic layer, said flange being of annular cylindricalshape and having an outside diameter substantially less than the insidediameter of said pressure tube whereby assembly of said piston into saidpressure tube is facilitated.

2. A shock absorber for a motor vehicle having a piston reciprocablewithin a pressure tube, said piston being of composite construction andhaving a metallic core with jounce and rebound flow passages, a plasticexterior layer surrounding the peripheral surface of said metallic core,said plastic layer having a cylindrical surface in slidable engagementwith said pressure tube, said surface having an exterior diametersubstantially equal to the interior diameter of said pressure tubewhereby only minimal clearance is provided between said piston and saidtube, said plastic layer having a depending annular flange ofsubstantial length relativ; to the total length of said plastic layer,said flange being of annular cylindrical shape and having an outsidediameter substantially less than the inside diameter of said pressuretube whereby assembly of said piston into said pressure tube isfacilitated, said metallic core having a peripheral upstanding flange onone of its ends and a depending peripheral flange on the other of itsends, said plastic layer having a first portion in interlockingrelationship with said upstanding flange, said plastic layer having asecond portion in interlocking relationship with said depending flange.

3. A shock absorber for a motor vehicle having a piston reciprocablewithin a pressure tube, said piston being of composite construction andhaving a metallic core with jounce and rebound flow passages, a plasticexterior layer surrounding the peripheral surface of said metallic core,said metallic core having a peripheral upstanding flange on one of itsends and a depending peripheral flange on the other of its ends,

defined in part by said upstanding flange, said plastic layer having afirst portion in interlocking relationship with said upstanding flangeand] said annular groove,

' equal to the inside diameter of said pressure tube said one end ofsaid core having an annular groove whereby only minimal clearance isprovided between said piston and said tube, said plastic layer having anannular flange depending from said second portion, said plastic annularflange being of substantial length relative to the total length of saidplastic layer, said flange being of annular cylindrical shape and havingan outside diameter substantially less than the inside diameter of saidpressure tube whereby assembly of said piston into said pressure tube isfacilitated.

4. A shock absorber for a motor vehicle having a piston reciprocablewithin a pressure tube, said piston being of composite construction andhaving a metallic core with jounce and rebound flow passages, a plasticexterior layer surrounding the peripheral surface of said metallic core,said plastic layer having a cylindrical surface in slidable engagementwith said pressure tube, said surface having an exterior diametersubstantially equal to the interior diameter of said pressure tubewhereby only minimal clearance is provided between said piston and saidtube, said plastic layer having an integral depending guide meansportion of substantial length relative to the total length of saidplastic layer, said guide means portion being normally spaced radiallyinwardly of the inner surface of said pressure tube whereby during themaking of said shock absorber said piston may be readily inserted intosaid pressure tube.

5. A shock absorber for a motor vehicle having a piston reciprocablewithin a pressure tube, said piston being of composite construction andhaving a metallic core with jounce and rebound flow passages, a plasticexterior layer surrounding the peripheral surface of said metallic core,said plastic layer having a first portion and a second portion ininterlocking relationship with the upper and lower peripheral edges ofsaid core, said plastic layer having a cylindrical bearing surface inslidable engagement with said pressure tube, said sur face having anexterior diameter substantially equal to the inside diameter of saidpressure tube whereby only minimal clearance is provided between saidpiston and said tube, said metallic core having a peripheral axiallyupstanding flange on one of its ends and an axially depending peripheralflange on the other of its ends, said plastic layer first portion beingin interlocking relationship with said upstanding flange, said plasticlayer second portion being in interlocking relationship with saiddepending flange.

6. A shock absorber for a motor vehicle according to claim 5 andincluding:

said one end of said core having an annular groove defined in part bysaid upstanding flange, said plastic layer first portion being ininterlocking relationship with said annular groove.

1. A shock absorber for a motor vehicle having a piston reciprocablewithin a pressure tube, said piston being of composite construction andhaving a metallic core with jounce and rebound flow passages, a plasticexterior layer surrounding the peripheral surface of said metallic core,said plastic layer having a cylindrical surface in slidable engagementwith said pressure tube, said surface having an exterior diametersubstantially equal to the interior diameter of said pressure tubewhereby only minimal clearance is provided between said piston and saidtube, said plastic layer having a depending annular flange ofsubstantial length relative to the total length of said plastic layer,said flange being of annular cylindrical shape and having an outsidediameter substantially less than the inside diameter of said pressuretube whereby assembly of said piston into said pressure tube isfacilitated.
 2. A shock absorber for a motor vehicle having a pistonreciprocable within a pressure tube, said piston being of compositeconstruction and having a metallic core with jounce and rebound flowpassages, a plastic exterior layer surrounding the peripheral surface ofsaid metallic core, said plastic layer having a cylindrical surface inslidable engagement with said pressure tube, said surface having anexterior diameter substantially equal to the interior diameter of saidpressure tube whereby only minimal clearance is provided between saidpiston and said tube, said plastic layer having a depending annularflange of substantial length relative to the total length of saidplastic layer, said flange being of annular cylindrical shape and havingan outside diameter substantially less than the inside diameter of saidpressure tube whereby assembly of said piston into said pressure tube isfacilitated, said metallic core having a peripheral upstanding flange onone of its ends and a depending peripheral flange on the other of itsends, said plastic layer having a first portion in interlockingrelationship with said upstanding flange, said plastic layer having asecond portion in interlocking relationship with said depending flange.3. A shock absorber for a motor vehicle having a piston reciprocablewithin a pressure tube, said piston being of composite construction andhaving a metallic core with jounce and rebound flow passages, a plasticexterior layer surrounding the peripheral surface of said metallic core,said metallic core having a peripheral upstanding flange on one of itsends and a depending peripheral flange on the other of its ends, saidone end of said core having an annular groove defined in part by saidupstanding flange, said plastic layer having a first portion ininterlocking relationship with said upstanding flange and said annulargroove, said plastic layer having a second portion in interlockingrelationship with said depending flange, said plastic layer having acylindrical portion of substantially uniform thickness situated betweensaid first and second portions, said cylindrical portion having asurface in slidable engagement with said pressure tube, said surfacehaving an exterior diameter substantially equal to the inside diameterof said pressure tube whereby only minimal clearance is provided betweensaid piston and said tube, said plastic layer having an annular flangedepending from said second portion, said plastic annular flange being ofsubstantial length relative to the total length of said plastic layer,said flange being of annular cylindrical shape and having an outsidediameter substantially less than the inside diameter of said pressuretube whereby assembly of said piston into said pressure tube isfacilitated.
 4. A shock absorber for a motor vehicle having a pistonreciprocable within a pressure tube, said piston being of compositeconstruction and having a metallic core with jounce and rebound flowpassages, a plastic exterior layer surrounding the peripheral surface ofsaid metallic core, said plastic layer having a cylindrical surface inslidable engagement with said pressure tube, said surface having anexterior diameter substantially equal to the interior diameter of saidpressure tube whereby only minimal clearance is provided between saidpiston and said tube, said plastic layer having an integral dependingguide means portion of substantial length relative to the total lengthof said plastic layer, said guide means portion being normally spacedradially inwardly of the inner surface of said pressure tube wherebyduring the making of said shock absorber said piston may be readilyinserted into said pressure tube.
 5. A shock absorber for a motorvehicle having a piston reciprocable within a pressure tube, said pistonbeing of composite construction and having a metallic core with jounceand rebound flow passages, a plastic exterior layer surrounding theperipheral surface of said metallic core, said plastic layer having afirst portion and a second portion in interlocking relationship with theupper and lower peripheral edges of said core, said plastic layer havinga cylindrical bearing surface in slidable engagement with said pressuretube, said surface having an exterior diameter substantially equal tothe inside diameter of said pressure tube whereby only minimal clearanceis provided between said piston and said tube, said metallic core havinga peripheral axially upstanding flange on one of its ends and an axiallydepending peripheral flange on the other of its ends, said plastic layerfirst portion being in interlocking relationship with said upstandingflange, said plastic layer second portion being in interlockingrelationship with said depending flange.
 6. A shock absorber for a motorvehiCle according to claim 5 and including: said one end of said corehaving an annular groove defined in part by said upstanding flange, saidplastic layer first portion being in interlocking relationship with saidannular groove.